The present invention relates to a method and apparatus for capturing magnetic resonance signals, recording medium and apparatus for magnetic resonance imaging using the same and more particularly to a method and apparatus for capturing magnetic resonance signal by using three-dimensional scanning, a recording medium for storing a program to execute such magnetic resonance imaging signal capturing method on a computer, as well as a magnetic resonance imaging apparatus having a means for capturing magnetic resonance imaging signals.
In MRI (magnetic resonance imaging) systems, the imaging principle consists of carrying a subject to be imaged into a bore in a ring magnet system of the magnetic resonance imaging apparatus, which is a space static magnetic field formed, applying a gradient magnetic field and a high frequency magnetic field thereto so as to generate spins to emit magnetic resonance signals, and reconstructing an image based on the signals received from the spins.
The gradient magnetic field will be applied in three axial directions each perpendicular to others. Three axes each perpendicular to others are a slice axis, phase axis, and frequency axis. The gradient magnetic field in the slice axis is a magnetic field, which enables the selective excitation of a desired slice on the slice axis by means of radio frequency (RF) excitation signals, and may also be called as a slice gradient. The gradient magnetic field in the phase axis is a magnetic field which enables a phase encoding of spins, and may also be called a chase encoding gradient. The gradient magnetic field in the frequency axis is a magnetic field, which enables reading out of magnetic resonance signals, which magnetic field may also be called as a read out gradient.
In a three-dimensional scanning, a slab, which is a slice of larger thickness, will be selectively excited so as to phase encode thereon in both phase axis and slice axis.
An error in the slice gradient may cause an erroneous position of the slab selectively excited. In such a case, the RF exciting frequency is to be modified so as to selectively excite a slice in a correct position. However, the reconstructed image may contain folding in the direction of slice axis.
It is therefore an object of the present invention to provide a method and apparatus for capturing magnetic resonance signals suitable for three dimensional scanning when there is an error in the slice gradient, a recording medium for storing a program to execute on a computer a function for capturing magnetic resonance signals, as well as a magnetic resonance imaging system incorporating a means for capturing magnetic resonance imaging signals.
To achieve the objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the present invention in one aspect provides:
(1) a method for capturing magnetic resonance signals, using a three dimensional scanning to selectively excite a slab with a gradient magnetic field and RF signals applied in the slice axis and to phase encode in a slice axis direction, characterized by comprising the steps of:
selectively exciting a slab by means of RF signals having a frequency compensated for in response to the error of the gradient magnetic field in the slice axis; and
phase encoding in the slice axis in the compensated phase corresponding to the compensation for the frequency.
The present invention in another aspect provides
(2) an apparatus for capturing magnetic resonance signals, using a three dimensional scanning by means of a static magnetic field, gradient magnetic field and high frequency magnetic field to selectively excite a slab with a gradient magnetic field and RF signals applied in the slice axis and to phase encode in a slice axis direction, characterized by comprising:
a selectively exciting means for selectively exciting a slab by means of RF signals having a frequency compensated for in response to the error of the gradient magnetic field In he slice axis; and
a phase encoding means for phase encoding in the slice axis * n the compensated phase corresponding to the compensation for the frequency.
The present invention in still another aspect provides
(3) a computer-readable recording medium for storing a program to be executed on a computer, using a three dimensional scanning by means of a static magnetic field, gradient magnetic field and high frequency magnetic field to selectively excite a slab with a gradient magnetic field and RF signals applied in the slice axis and to phase encode in a slice axis direction, said program characterized by comprising the steps of:
selectively exciting a slab by means of RF signals having a frequency compensated for in response to the error of the gradient magnetic field in the slice axis; and
phase encoding in the slice axis in the compensated phase corresponding to the compensation for the frequency.
The present invention in yet another aspect provides
(4) a magnetic resonance imaging system, for capturing magnetic resonance imaging signals by using a three dimensional scanning by means of a static magnetic field, gradient magnetic field and high frequency magnetic field to selectively excite a slab with a gradient magnetic field and RF signals applied in the slice axis and to phase encode in a slice axis direction, in order to reconstruct an image based on thus captured signals, the system for capturing magnetic resonance imaging signals characterized by comprising:
a selectively exciting means for selectively exciting a slab by means of RF signals having a frequency compensated for in response to the error of the gradient magnetic field in the slice axis; and
a phase encoding means for chase encoding in the slice axis in the compensated phase corresponding to the compensation for the frequency.
In the above aspects of the present invention, proper magnetic resonance signals may be captured in he three dimensional scanning when there is an error in the slice gradient, since a slab is selectively excited by RF signals having a frequency compensated for in response to the error in the gradient magnetic field in the slice axis and phase encoded in the slice axis direction.
In accordance with the present invention, a method and apparatus for appropriately capturing magnetic resonance signals in three dimensional scanning when there is an error in the slice gradient, a recording medium that stores a program for executing on a computer the functionality of capturing the magnetic resonance signals, as well as a system for magnetic resonance imaging incorporating means for capturing magnetic resonance signals can be achieved.